It will draw as many as many watt it needed....
as posters above said u will experience system instability when the PSU not supply enough power (like random shutdown, etc...) so why do you think it not supply enough?
The answer for your question is : No, u cannot allocate it more (technically, u can if u had multi rail system u can switch the rail to not used rail, but it depends the ampere of the PSU had.......)
so if u think it not enough, then better PSU is needed